This invention relates generally to the field of fluid drop generation and the application thereof to jet drop recorders of the type shown in U.S. Pat. No. 3,701,998 to Mathis, issued Oct. 31, 1972. In recorders of this type, there are a pair of rows of orifices which receive an electrically conductive recording fluid, such as for instance a water base ink, from a pressurized fluid manifold and eject the fluid in two rows of parallel streams. The fluid flows through orifices in a plate with the formation of drops being stimulated by the application of a series of traversing waves to the plate. This method of drop generation is more completely described in U.S. Pat. No. 3,739,393 to Lyon et al, issued June 12, 1973.
Graphic reproduction in recorders of this type is accomplished by selectively charging and deflecting some of the drops in each of the streams and thereafter disposing the uncharged drops on a moving web of paper or other material. Charging is accomplished by application of binary charge control signals to charging electrodes near the edge of the streams. As the drops separate from their parent fluid filaments, they carry a portion of the charge applied by the charging electrodes. Thereafter the drops pass through electrostatic fields which have no effect upon the charged drops but which cause the charged drops to be deflected for catching by one or the other of a pair of catchers which service the rows of streams.
U.S. Pat. No. 3,787,883 to Cassill, issued Jan. 22, 1974, discloses apparatus for creating the deflecting electrostatic fields. A thin deflection ribbon is positioned between and parallel to the two rows of parallel drop streams with the catchers positioned outwardly of the drop streams. A voltage is applied between the deflection ribbon and the catchers such that charged ink drops will be deflected to one of the two catchers.
The apparatus generating the fluid drops may also occasionally generate droplets of small size which form an ink mist. While very little of this mist will be present at any time, ink build-up on various surfaces of the printer may result over a long period of time. An unwanted ink mist in the printer may also result from crooked ink jets or from difficulties encountered in starting up or shutting down the printer. One approach taken to avoid build-up on the upper surface of a catcher is shown in U.S. Pat. No. 3,777,307 to Duffield, issued Dec. 4, 1973 in which a catcher having a porous upper surface is disclosed. A compartment within the catcher is connected to a vacuum source such that ink on the upper surface of the catcher is drawn into the compartment and then drawn off.
When the type of ink jet printer having a number of deflection electrodes surrounding each stream of ink drops, it is known to provide grooves in the electrodes. The ink droplets deposited on the electrodes are drawn into the grooves and transported away from the electrode surface by virtue of the capillary action of the grooves.
Heretofore ink mist build-up on a deflection ribbon has generally been avoided through periodic cleaning of the ribbon. This cleaning requires that the printing operation be temporarily stopped and is thus inconvenient as well as expensive. If the mist of conductive ink were permitted to build-up, however, the electrical efficacy of the ribbon would be gradually altered. Such a build-up may increase the likelihood of a short between the catchers and the ribbon or may interfere with the operation of the ink jets. To avoid these disadvantages, a porous deflection ribbon has been developed and is the subject of U.S. Pat. application Ser. No. 653,194, filed Jan. 28, 1976 and assigned to the assignee of the present invention. A deflection ribbon of constant porosity along its length is somewhat disadvantageous, however, in that the liquid ingestion characteristics of the ribbon will vary greatly.